Cron Expression Generator

Frequently asked questions

• What is a cron expression?

  A cron expression is a five-field schedule string used by the cron daemon on Linux and Unix systems: minute (0-59), hour (0-23), day of month (1-31), month (1-12) and day of week (0-7, where both 0 and 7 mean Sunday). For example, 0 9 * * 1-5 means "at 09:00 on weekdays".

• How do I run a cron job every 5 minutes?

  Use */5 * * * *. The */5 in the minute field means "every value divisible by 5", so the job runs at minute 0, 5, 10 and so on of every hour. The same pattern works for other intervals: */15 for every 15 minutes, */30 for every half hour.

• What do the asterisk, comma, dash and slash mean in cron?

  An asterisk (*) matches every value of a field. A comma separates a list (1,15 means the 1st and the 15th). A dash defines a range (1-5 means Monday to Friday in the weekday field). A slash defines a step (*/10 means every 10th value). They can be combined, such as 0-30/10 for minutes 0, 10, 20 and 30.

• Why is my cron job set for both a day of month and a weekday running too often?

  Classic cron treats a restricted day-of-month and a restricted day-of-week as OR, not AND. The expression 0 0 1 * 1 runs at midnight on the 1st of the month AND on every Monday, not only on Mondays that fall on the 1st. This surprises almost everyone at least once.

• Are cron times in my timezone?

  Cron runs in the timezone of the machine where the crontab lives, which is often UTC on servers. The next-run preview on this page uses your browser timezone, so if your server runs on UTC the actual execution moment can differ. Check the server timezone with the date command before scheduling time-sensitive jobs.

• What is the difference between 5-field and 6-field (Quartz) cron?

  Standard Unix cron uses 5 fields starting with the minute. Quartz, used by many Java schedulers and some cloud platforms, adds a seconds field at the front and an optional year at the end, and uses extra characters like ?, L, W and #. This tool speaks standard 5-field cron: paste a Quartz expression and it will tell you to drop the seconds field.

• Can I run a cron job on the last day of the month?

  Not directly: standard cron has no "last day" syntax (the L character is a Quartz extension). The common workaround is to schedule the job for days 28 to 31 and let the script exit early unless tomorrow is the 1st. Some modern schedulers and managed cron services support last-day natively.

• Do shortcuts like @daily and @hourly work?

  Most cron implementations support the macros @hourly (0 * * * *), @daily or @midnight (0 0 * * *), @weekly (0 0 * * 0), @monthly (0 0 1 * *) and @yearly or @annually (0 0 1 1 *). There is also @reboot, which runs once at system startup and has no fixed schedule. This page understands all of them.

• How do I schedule a cron job every hour?

  Use 0 * * * *, which runs at minute 0 of every hour. To run at a different minute, change the first field: 30 * * * * runs at half past every hour. For every few hours, use a step in the hour field: 0 */6 * * * runs at midnight, 06:00, 12:00 and 18:00.

• How do I run a cron job every day at a specific time?

  Set the minute and hour fields and leave the rest as asterisks. 0 0 * * * runs every day at midnight, 0 8 * * * at 08:00, 30 23 * * * at 23:30. Remember that the time is interpreted in the server timezone, not yours.

• Why did my cron job not run?

  The usual suspects: the cron daemon has a minimal environment (PATH is short, so use absolute paths), the script is not executable, the server timezone differs from yours, percent signs need escaping in crontabs, or the job failed silently. Because cron reports nothing by default, the reliable fix is heartbeat monitoring: the job pings a URL when it finishes, and you get alerted when the ping does not arrive.